Alkali metals Group atomic radii

It is possible to explain these trends in terms of the electron configurations of the corresponding atoms. Consider first the increase in radius observed as we move down the table, let us say among the alkali metals (Group 1). All these elements have a single s electron outside a filled level or filled p sublevel. Electrons in these inner levels are much closer to the nucleus than the outer s electron and hence effectively shield it from the positive charge of the nucleus. To a first approximation, each inner electron cancels the charge of one pro-... 

Figure 8.10 Periodicity of atomic radius. A plot of atomio radius vs. atomic numberforthe elements in Periods 1 through 6 shows a periodic change the radius generally decreases through a period to the noble gas [Group 8A(18) purple] and then increases suddenly to the next alkali metal [Group 1 A(1) brown]. Deviation from the general deorease occurs among the transition elements.

These three structures are the predominant structures of metals, the exceptions being found mainly in such heavy metals as plutonium. Table 6.1 shows the structure in a sequence of the Periodic Groups, and gives a value of the distance of closest approach of two atoms in the metal. This latter may be viewed as representing the atomic size if the atoms are treated as hard spheres. Alternatively it may be treated as an inter-nuclear distance which is determined by the electronic structure of the metal atoms. In the free-electron model of metals, the structure is described as an ordered array of metallic ions immersed in a continuum of free or unbound electrons. A comparison of the ionic radius with the inter-nuclear distance shows that some metals, such as the alkali metals are empty i.e. the ions are small compared with the hard sphere model, while some such as copper are full with the ionic radius being close to the inter-nuclear distance in the metal. A consideration of ionic radii will be made later in the ionic structures of oxides. 

Symbol Cs atomic number 55 atomic weight 132.905 a Group lA (Group 1) alkali metal element electron configuration [Xe]6si atomic radius 2.65 A ionic radius (Cs ) 1.84 A ionization potential 3.89 eV valence +1 natural isotope Cs-133 37 artificial isotopes ranging in mass numbers from 112 to 148 and half-lives 17 microseconds (Cs-113) to 2.3x10 years (Cs-135). 

Symbol Rb atomic number 37 atomic weight 85.468 a Group I (Group 1) alkali metal element electron configuration [Kr] 5si valence -i-l atomic radius 2.43A ionic radius, Rb+ 1.48A atomic volume 55.9 cc/g-atom at 20°C ionization potential 4.177 V standard electrode potential Rb+ + e Rb, E° = -2.98V two naturally-occurring isotopes, Rb-85 (72.165%) and Rb-87 (27.835%) Rb-87 radioactive, a beta emitter with a half-bfe 4.88xl0i° year twenty-seven artificial radioactive isotopes in the mass range 74—84, 86, 88-102. 

Symbol Na atomic number 11 atomic weight 22.9898 a Group lA (Group 1) alkali metal element electron configuration [NejSs valence +1 atomic radius 1.85A ionic radius, Na" in crystals 1.02A (for a coordination number 6) ionization potential 5.139 eV standard electrode potential, E°(Na+ + e Na) -2.71 V one naturally-occurring stable isotope, Na-23 (100%) sixteen artificial radioactive isotopes in the mass range 19-22, 24—35 longest-lived radioisotope, Na-22, ti/2 2.605 year shortest-lived isotope Na-35, ti/2 1.5 ms. 

Some important properties of the first five alkali metals are shown in Table 12.9. The data in Table 12.9 show that when we move down the group, the first ionization energy decreases and the atomic radius increases. This agrees with the general trends discussed in Section 12.15. 

The ionization potentials (IPs) of ammonia clusters containing alkali metal atoms, such as Li [10], Na [8] and Cs [9], have been reported by Hertel s and Fuke s groups. These clusters have been prepared by pickup sources coupled with a heated oven (Na and Cs) or a laser-vaporization source (Li). The IP(n) values decrease almost linearly with (n-f 1) , which is approximately proportional to the inverse of the cluster radius. Although the IPs of free atoms are different (5.392, 5.139 and 3.894 eV for Li, Na and Cs, respectively), those of the clusters (n > 5) are almost the same irrespective to the metal atoms. The intercept at (n + 1) 0... 

There are a number of trends to note. In the well-behaved alkali metals and alkaline earth metals, the radius of an atom increases smoothly as the atomic number increases. The transition metals all have rather similar radii as one passes along the period, and these increase slightly with atomic number going down a group. The same is true for the lanthanides and actinides. 

Within a group of elements we find that atomic radius increases with increasing atomic nnmber. For the alkali metals in Group lA, the outermost electron resides in the ns orbital. Since orbital size increases with the increasing principal quantum number n, the size of the metal atoms increases from Li to Cs. We can apply the same reasoning to the elements in other groups. 

In Figure 1- 10 it is seen that the relative atomic radius for the elements in the F main group (alkali metals) increases which is the case for all vertically groups. 

The physical properties of metal alkoxides depend primarily on the characteistics of the metal (e.g., the electronegativity, valence, atomic radius, and coordination number) and secondarily on the characteristics of the alkyl group (e.g., the size and shape). There is a change from the solid, nonvolatile ionic alkoxides of some of the alkali metals to the volatile covalent liquids of elements of valence 3, 4, 5, or 6 (e.g., Al, Si, Ti, Zr, Sb, and Te), whereas alkoxides of metals with intermediate electronegativities, such as La and Y, are mainly solids (Table 5.1). 

Within a group of elements we find that atomic radius increases with increasing atomic number. For the alkali metals in Group lA, the outermost electron resides in... 

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